Search

Interplanetary human missions to Mars and beyond will suppose a very demanding physical and psychological environment for future astronauts. Isolation, confinement, hypoxia or hypercapnia in a less pressurized atmosphere, darkness and other factors are expected to endanger a mission's success, directly influencing human performance. In order to study the effects of such environmental conditions on human beings, the SIMSKILL Experiment aims to investigate how spacecraft piloting performance decays over time by deploying a Soyuz flight simulator on the Antarctic research stations Halley VI and Concordia, which feature similar living conditions as those of a space mission, leading eventually to muscular atrophy, loss of cognitive capacities, and reduction of psycho-motor skills. This paper offers an analysis on the recorded data from the scientific campaigns in Antarctica, compared to those of the subjects in a control group in Stuttgart, Germany. An overall total of 69 subjects and more than one thousand approach and docking flights to the ISS performed in a Soyuz-TMA simulator have been analysed using a performance assessment methodology. The post-processed simulation dataset allows to recognize collective trends and find which are the essential parameters that affect the pilot's skill evolution. The results obtained from this analysis show how the influence of isolation, confinement and hypoxia in Antarctica is crucial to understand how differences in performance appear between subjects. The significance of the obtained results has been proven by means of statistical models, which show that a one-month training refreshing delivers satisfactory performance for a docking simulation, whereas a frequency of 3 months follows to a loss of piloting reliability. Moreover, the effect of isolation and hypoxia aggravates the loss of flight performance.

Adult neurogenesis persists in mammals in the neurogenic zones where newborn neurons are incorporated into existing neuronal circuits. Relevant molecular elements of the neurogenic niches include the family of Cell Adhesion Molecules (CAM), which participate in signal transduction and regulate radial glial progenitor's (RGPs) survival, division and differentiation. The Neural Cell Adhesion Molecule 2 (NCAM2) is expressed in brain development and in adult stages, and controls dendrite arborisation and synaptic formation and maintenance during development. Nevertheless, the role of NCAM2 in neurogenesis and lineage progression is not well understood. Here we analyse the functions of NCAM2 in the regulation of RGPs in adult neurogenesis in the dentate gyrus and during corticogenesis, by using different lentiviral-mediated genetic approaches to modulate its expression, both in vivo and in vitro. First, we characterized the expression of NCAM2 among the main actors of the neurogenic process revealing different levels of NCAM2 amid the progression of RGPs and the formation of juvenile neurons. Further, we show that overexpression of NCAM2 arrest infected cells in a RGP-like state, with characteristic morphological, immunocytochemical and electron microscopy features. In contrast, NCAM2 overexpression in embryonic cortical progenitors does not seems to alter cell fate, but causes transient migration deficits. These results reveal a differential role of NCAM2 in the regulation of adult and embryonic RGPs, and specifically, a significant implication of NCAM2 in the regulation and progression of RGPs during adult neurogenesis in the hippocampus.

Synaptic plasticity involves structural modifications in dendritic spines that are modulated by local protein syn-thesis and actin remodeling. Here, we investigated the molecular mechanisms that connect synaptic stimulation to these processes. We found that the phosphorylation of isoform-specific sites in eEF1A2—an essential transla-tion elongation factor in neurons—is a key modulator of structural plasticity in dendritic spines. Expression of a nonphosphorylatable eEF1A2 mutant stimulated mRNA translation but reduced actin dynamics and spine density. By contrast, a phosphomimetic eEF1A2 mutant exhibited decreased association with F-actin and was inactive as a translation elongation factor. Activation of metabotropic glutamate receptor signaling triggered transient dissociation of eEF1A2 from its regulatory guanine exchange factor (GEF) protein in dendritic spines in a phosphorylation-dependent manner. We propose that eEF1A2 establishes a cross-talk mechanism that coordinates translation and actin dynamics during spine remodeling, This work was funded by a grant from the Ministry of Economy and Competitiveness of Spain and the European Union (FEDER) (BFU2017-83375-R) to C.G. D.F.M. received an FI fellowship from Generalitat de Catalunya. F.K.M., M. Dodel, and M. Dermit were supported by a fellowship from the Medical Research Council of United Kingdom (grant ref. MR/P009417/1).

Manipulation of neuronal activity using two-photon excitation of azobenzene photoswitches with near-infrared light has been recently demonstrated, but their practical use in neuronal tissue to photostimulate individual neurons with three-dimensional precision has been hampered by firstly, the low efficacy and reliability of NIR-induced azobenzene photoisomerization compared to one-photon excitation, and secondly, the short cis state lifetime of the two-photon responsive azo switches. Here we report the rational design based on theoretical calculations and the synthesis of azobenzene photoswitches endowed with both high two-photon absorption cross section and slow thermal back-isomerization. These compounds provide optimized and sustained two-photon neuronal stimulation both in light-scattering brain tissue and in Caenorhabditis elegans nematodes, displaying photoresponse intensities that are comparable to those achieved under one-photon excitation. This finding opens the way to use both genetically targeted and pharmacologically selective azobenzene photoswitches to dissect intact neuronal circuits in three dimensions., Two-photon absorption capacity of azobenzene photoswitches usually comes with a reduction in thermal stability. Here, the authors developed photoswitches with high two-photon sensitivity and enhanced cis isomer thermal lifetime for the control of glutamate receptors.

International audience; Glycine receptors (GlyRs) are indispensable for maintaining excitatory/inhibitory balance in neuronal circuits that control reflexes and rhythmic motor behaviors. Here we have developed Glyght, a GlyR ligand controlled with light. It is selective over other Cys-loop receptors, is active in vivo, and displays an allosteric mechanism of action. The photomanipulation of glycinergic neurotransmission opens new avenues to understanding inhibitory circuits in intact animals and to developing drug-based phototherapies.

Synaptic plasticity involves structural modifications in dendritic spines. Increasing evidence suggests that structural plasticity is modulated by local protein synthesis and actin remodeling in a synapsis-specific manner. However, the precise molecular mechanisms connecting synaptic stimulation to these processes in dendritic spines are still unclear. In the present study, we demonstrate that the configuration of phosphorylation sites in eEF1A2, an essential translation elongation factor in neurons, is a key modulator of structural plasticity in dendritic spines. A mutant that cannot be phosphorylated stimulates translation but reduces actin dynamics and spine density. By contrast, the phosphomimetic variant loosens its association with F-actin and becomes inactive as a translation elongation factor. Metabotropic glutamate receptor signaling triggers a transient dissociation of eEF1A2 from its GEF protein in dendritic spines, in a phospho-dependent manner. We propose that eEF1A2 establishes a crosstalk mechanism that coordinates local translation and actin dynamics during spine remodeling.

Background: Autologous chimeric antigen receptor-T (CAR-T) cells that target BCMA (BCMA-CARs) have emerged as a promising treatment for multiple myeloma (MM). Current clinical protocols dictate that BCMA-CAR therapy is only used after patients have repeatedly relapsed. However, at this stage, the immunosuppressive nature of advanced MM and/or side-effects of the previous therapies cause T cell dysfunction and an unfavourable phenotype, such as exhaustion, senescence and loss of early memory cells. An alternative and convenient pool of 'fitter' T cells are apheresis products that are routinely collected to obtain progenitor cells for autologous stem cell transplantation (ASCT), an intervention that is often carried out early in MM treatment. However, to mobilise the progenitor cells, patients are treated with G-CSF, which could have negative effects on T cells such as reduce proliferation, impair CD8 + T cell function and induce regulatory T cell (Treg) expansion. Whether this has an effect on the BCMA-CARs generated from these T cells, however, is unknown. Therefore, we aimed to establish whether G-CSF treatment had detrimental effects on T cell phenotype, and moreover, to ascertain whether BCMA-CARs that are generated from these T cells were impaired compared to those produced from T cells prior to G-CSF infusion. Methods: T cells were isolated from the blood of 9 patients with MM before and after 4 days of subcutaneous G-CSF administration (PRE G-CSF and POST G-CSF, respectively) prior to peripheral blood CD34 + cell harvesting for an ASCT as consolidation after first-line induction treatment. Following stimulation with anti-CD3/anti-CD28 beads and IL-2, T cells were transduced with ARI2h, an anti-BCMA CAR produced at our institution that is currently being explored in a clinical trial for relapsed/refractory MM (NCT04309981). Freshly-isolated T cells or expanded ARI2h cells were analysed by flow cytometry for markers of cell identity, activation, dysfunction and memory, or alternatively, challenged with an MM cell line (ARP-1 or U266) and then tested for cytokine production and cytotoxic ability. In addition, PRE and POST G-CSF ARI2h CARs were injected into ARP-1 tumour-bearing mice to assess their in vivo function. Results: Firstly, the phenotype of PRE G-CSF and POST G-CSF T cells, before CAR production, was analysed to identify effects of G-CSF treatment. Interestingly, there were fewer POST G-CSF CD8 + T cells with a stem cell memory (CCR7 +CD45RA +CD95 +) phenotype, but the proportion of naïve (CCR7 +CD45RA +CD95 -) cells and other memory populations was not significantly different. Moreover, POST G-CSF T cells had a lower CD4:CD8 ratio, but did not contain more senescent-like cells or display evidence of pre-activation or increased expression of exhaustion markers. Due to the known effect of G-CSF on CD4 + Treg expansion, the percentage of Tregs was also compared between the PRE G-CSF and POST G-CSF samples, but no difference was observed. Following T-cell activation and CAR transduction, comparable transduction efficiencies and proliferation rates were obtained. Likewise, the in vitro function of PRE G-CSF and POST G-CSF ARI2h cells, as determined by assessing their cytotoxic response to MM cell lines and ability to produce effector molecules such as granzyme B, was similar. To test the in vivo function of ARI2h CAR-T cells expanded from PRE G-CSF and POST G-CSF samples, they were injected into a murine xenograft model of advanced MM. Mice administered with both PRE and POST G-CSF ARI2h cells survived longer than those given untransduced T cells (p=0.015 and p=0.039, respectively), but there was no difference in the longevity of mice between the PRE G-CSF and POST G-CSF groups (p=0.990) (Figure 1). The similarity of the in vitro and in vivo function of PRE and POST G-CSF ARI2h cells was reflected in the phenotype of the CAR-T cells after ex vivo expansion, with cells from both groups displaying equal levels of activation, exhaustion, and importantly for CAR-T cell activity, memory/effector phenotype. Conclusions: The in vitro and in vivo functions of ARI2h CAR-T cells when generated from either PRE G-CSF or POST G-CSF samples were comparable, despite G-CSF administration decreasing the CD8 + stem cell memory pool. Overall, we conclude that T cells from apheresis products, performed to collect G-CSF-mobilised peripheral blood progenitor cells for ASCT, are suitable for BCMA-CAR manufacture. Figure 1 Figure 1. Disclosures Lozano: Grifols: Honoraria; Terumo BCT: Honoraria, Research Funding; Macopharma: Research Funding. Fernandez de Larrea: BMS: Consultancy, Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Takeda: Honoraria, Research Funding; GSK: Honoraria; Sanofi: Consultancy; Janssen: Consultancy, Honoraria, Research Funding.

Glycine receptors (GlyRs) are indispensable to maintain excitatory/inhibitory balance in neuronal circuits controlling reflex and rhythmic motor behaviors. Here we have developed Glyght, the first GlyR ligand controlled with light. It is selective over other cys-loop receptors, active in vivo, and displays an allosteric mechanism of action. The photomanipulation of glycinergic neurotransmission opens new avenues to understand inhibitory circuits in intact animals, and to develop drug-based phototherapies.

The physiological activity of proteins is often studied with loss-of-function genetic approaches, but the corresponding phenotypes develop slowly and can be confounding. Photopharmacology allows direct, fast, and reversible control of endogenous protein activity, with spatiotemporal resolution set by the illumination method. Here, we combine a photoswitchable allosteric modulator (alloswitch) and 2-photon excitation using pulsed near-infrared lasers to reversibly silence metabotropic glutamate 5 (mGlu5) receptor activity in intact brain tissue. Endogenous receptors can be photoactivated in neurons and astrocytes with pharmacological selectivity and with an axial resolution between 5 and 10 μm. Thus, 2-photon pharmacology using alloswitch allows investigating mGlu5-dependent processes in wild-type animals, including synaptic formation and plasticity, and signaling pathways from intracellular organelles. © 2019 National Academy of Sciences. All rights reserved., ACKNOWLEDGMENTS. We thank Jordi Hernando (Autonomous University of Barcelona) for useful discussions on 2-photon excitation; Pere Català (Utrecht University) for help with GCaMP; Francisco Ciruela (University of Barcelona) for mGlu5-eYFP plasmid; Erin Schuman and Stephan Junek (Max Planck Institute for Brain Research, Frankfurt) for preliminary 2-photon excitation experiments; and Ashraf Muhaisen (University of Barcelona) for help with slicing. This research received funding from European Union Research and Innovation Programme Horizon 2020 [Human Brain Project SGA2 Grant Agreement 785907 (WaveScalES)], European Research ERA-Net SynBio programme (Modulightor project), and financial support from Agency for Management of University and Research Grants/Generalitat de Catalunya (CERCA Programme; 2017-SGR-1442 project), Fonds Européen de Développement Économique et Régional (FEDER) funds, Ministry of Economy and Competitiveness (MINECO)/FEDER (Grant CTQ2016-80066-R), and the Fundaluce foundation. S.P. was supported by an FI fellowship from the Agency for Management of University and Research Grants/Generalitat de Catalunya (2014FI_B2 00160). H.L. was supported by an Institute for Bioengineering of Catalonia Severo Ochoa International PhD Programme fellowship from MINECO. M.B. was supported by a H2020-MSCA-IF Reintegration Grant. K.E.P. receives support from NIH/National Institute of Neurological Disorders and Stroke Grant R01NS099254 and NSF Biophotonics Grant 1604544. E.S. receives support from MINECO (Grant SAF2016-7426).

Many neurodevelopmental disorders are characterized by impaired functional synaptic plasticity and abnormal dendritic spine morphology, but little is known about how these are related. Previous work in the Fmr1-/y mouse model of fragile X (FX) suggests that increased constitutive dendritic protein synthesis yields exaggerated mGluR5-dependent long-term synaptic depression (LTD) in area CA1 of the hippocampus, but an effect on spine structural plasticity remains to be determined. In the current study, we used simultaneous electrophysiology and time-lapse two photon imaging to examine how spines change their structure during LTD induced by activation of mGluRs or NMDA receptors (NMDARs), and how this plasticity is altered in Fmr1-/y mice. We were surprised to find that mGluR activation causes LTD and AMPA receptor internalization, but no spine shrinkage in either wildtype or Fmr1-/y mice. In contrast, NMDAR activation caused spine shrinkage as well as LTD in both genotypes. Spine shrinkage was initiated by non-ionotropic (metabotropic) signaling through NMDARs, and in wild-type mice this structural plasticity required activation of mTORC1 and new protein synthesis. In striking contrast, NMDA-induced spine plasticity in Fmr1-/y mice was no longer dependent on acute activation of mTORC1 or de novo protein synthesis. These findings reveal that the structural consequences of mGluR and metabotropic NMDAR activation differ, and that a brake on spine structural plasticity, normally provided by mTORC1 regulation of protein synthesis, is absent in FX. Increased constitutive protein synthesis in FX appears to modify functional and structural plasticity induced through different glutamate receptors.

Activity-dependent plasticity of synaptic structure and function plays an essential role in neuronal development and in cognitive functions including learning and memory. The formation, maintenance and modulation of dendritic spines are mainly controlled by the dynamics of actin filaments (F-actin) through interaction with various actin-binding proteins (ABPs) and postsynaptic signaling messengers. Induction of long-term potentiation (LTP) triggers a cascade of events involving Ca2+ signaling, intracellular pathways such as cAMP and cGMP, and regulation of ABPs such as CaMKII, Cofilin, Aip1, Arp2/3, α-actinin, Profilin and Drebrin. We review here how these ABPs modulate the rate of assembly, disassembly, stabilization and bundling of F-actin during LTP induction. We highlight the crucial role that CaMKII exerts in both functional and structural plasticity by directly coupling Ca2+ signaling with F-actin dynamics through the β subunit. Moreover, we show how cAMP and cGMP second messengers regulate postsynaptic structural potentiation. Brain disorders such as Alzheimer's disease, schizophrenia or autism, are associated with alterations in the regulation of F-actin dynamics by these ABPs and signaling messengers. Thus, a better understanding of the molecular mechanisms controlling actin cytoskeleton can provide cues for the treatment of these disorders. info:eu-repo/semantics/publishedVersion

The present paper investigates the long-term functionality of an ex vivo gene therapy approach based on cell microencapsulation for the continuous delivery of erythropoietin (EPO) without implementation of immunosuppressive protocols. Polymer microcapsules (0.5 ml) loaded with EPO-secreting C(2)C(12) myoblasts and releasing 15,490 +/- 600 IU EPO/24 h were implanted in the peritoneum and subcutaneous tissue of syngeneic and allogeneic mice. High and constant hematocrit levels were maintained for more than 100 days in all implanted mice. Capsules retrieved from the peritoneum were free-floating or forming small capsule clusters, and we detected only a weak fibroblast outgrowth in capsules adhered to organs, whereas capsules explanted from the subcutaneous region appeared altogether as a richly vascularized structure with no signs of major host reaction. Interestingly, the functionality of capsules implanted in the allogeneic mice persisted until day 210 after implantation. These results highlight the feasibility of cell encapsulation technology for the long-term delivery of EPO independent of the method of administration and the mouse strain.

Dysfunction of dopaminergic neurons may contribute to motor impairment in Huntington's disease. Here, we study the role of brain-derived neurotrophic factor (BDNF) in alterations of the nigrostriatal system associated with transgenics carrying mutant huntingtin. Using huntingtin-BDNF+/- double-mutant mice, we analyzed the effects of reducing the levels of BDNF expression in a model of Huntington's disease (R6/1). When compared with R6/1 mice, these mice exhibit an increased number of aggregates in the substantia nigra pars compacta. In addition, reduction of BDNF expression exacerbates the dopaminergic neuronal dysfunction seen in mutant huntingtin mice, such as the decrease in retrograde labelling of dopaminergic neurons and striatal dopamine content. However, mutant huntingtin mice with normal or lowered BDNF expression show the same decrease in the anterograde transport, number of dopaminergic neurons and nigral volume. In addition, reduced BDNF expression causes decreased dopamine receptor expression in mutant huntingtin mice. Examination of changes in locomotor activity induced by dopamine receptor agonists revealed that, in comparison with R6/1 mice, the double mutant mice exhibit lower activity in response to amphetamine, but not to apomorphine. In conclusion, these findings demonstrate that the decreased BDNF expression observed in Huntington's disease exacerbates dopaminergic neuronal dysfunction, which may participate in the motor disturbances associated with this neurodegenerative disorder.

The implementation of cell replacement therapies for Huntington's disease using multipotent neural stem cells (NSCs) requires the specific differentiation into γ-aminobutyric acid (GABA) neuronal subtype before transplantation. Here we present an efficient culture procedure that induces stable GABAergic neurons from the immortalized striatal neural stem cell line ST14A. This process requires sequential retinoic acid treatment and KCl depolarization. Initial addition of 10 μM retinoic acid increased cell survival and promoted neuronal differentiation. Subsequent stimulation with 40 mM KCl induced specific differentiation into GABAergic neurons, yielding 74% of total cultured cells. KCl-evoked Ca2+ influx reduced cell proliferation and nestin expression, and induced neurite outgrowth and GABAergic markers as well as GABA contents, release, and uptake. Characterization of the integration, survival, and phenotype of these predifferentiated GABAergic neurons following transplantation into the adult brain in a model of Huntington's disease revealed long-term survival in quinolinate-lesioned striata. Under these conditions, cells maintained their GABAergic phenotype and elaborated neurite processes with synaptic contacts with endogenous neurons. In conclusion, we have generated a homogeneous population of functional GABAergic neurons from a neural stem cell line, which survive and maintain their acquired fate in vivo. These data may lend support to the possibility of cell replacement therapies for Huntington's disease using neural stem cells., This study was supported by the Ministerio de Ciencia y Tecnología (SAF2002-00314, J.A.; SAF2002-00311, J.M.C. Spain), ‘redes temáticas de investigación coorporativa’ (G03/167; G03/210; Ministerio de Sanidad y Consumo, Spain), and Fundació La Caixa. M.B. is a fellow of the Universitat de Barcelona (Spain) and J.R.P. of the Ministerio de Educación, Cultura y Deporte (Spain).

Synapses store information by long-lasting modifications of their structure and molecular composition, but the precise chronology of these changes has not been studied at single-synapse resolution in real time. Here we describe the spatiotemporal reorganization of postsynaptic substructures during long-term potentiation (LTP) at individual dendritic spines. Proteins translocated to the spine in four distinct patterns through three sequential phases. In the initial phase, the actin cytoskeleton was rapidly remodeled while active cofilin was massively transported to the spine. In the stabilization phase, cofilin formed a stable complex with F-actin, was persistently retained at the spine, and consolidated spine expansion. In contrast, the postsynaptic density (PSD) was independently remodeled, as PSD scaffolding proteins did not change their amount and localization until a late protein synthesis-dependent third phase. Our findings show how and when spine substructures are remodeled during LTP and explain why synaptic plasticity rules change over time., RIKEN Brain Science Institute, National Institutes of Health (U.S.) (Grant R01DA17310), Human Frontier Science Program (Strasbourg, France), Paul and Anne Punzak Marcus Fund

We report the characterization of tris(2-pyridylmethyl)amine (TPA) as a membrane-permeable zinc chelator for intercepting biological mobile zinc. Compared to N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), TPA chelates zinc with faster kinetics in cuvettes, live cells, and brain slices. TPA also is generally less toxic than TPEN in cell culture. Mechanistic analysis indicates that these improvements arise from both the electronic and steric properties of TPA including weaker metal-binding affinity, lower pK[subscript a], and smaller size. These results demonstrate that TPA chelation is a valuable addition to the methodologies available for investigating mobile zinc in biology., National Institute of General Medical Sciences (U.S.) (Grant GM065519), FRAXA Research Foundation (Fellowship)

Dendritic spines are small mushroom-like protrusions arising from neurons where most excitatory synapses reside. Their peculiar shape suggests that spines can serve as an autonomous postsynaptic compartment that isolates chemical and electrical signaling. How neuronal activity modifies the morphology of the spine and how these modifications affect synaptic transmission and plasticity are intriguing issues. Indeed, the induction of long-term potentiation (LTP) or depression (LTD) is associated with the enlargement or shrinkage of the spine, respectively. This structural plasticity is mainly controlled by actin filaments, the principal cytoskeletal component of the spine. Here we review the pioneering microscopic studies examining the structural plasticity of spines and propose how changes in actin treadmilling might regulate spine morphology.

Animals can make faster behavioral responses to multisensory stimuli than to unisensory stimuli. The superior colliculus (SC), which receives multiple inputs from different sensory modalities, is considered to be involved in the initiation of motor responses. However, the mechanism by which multisensory information facilitates motor responses is not yet understood. Here, we demonstrate that multisensory information modulates competition among SC neurons to elicit faster responses. We conducted multiunit recordings from the SC of rats performing a two-alternative spatial discrimination task using auditory and/or visual stimuli. We found that a large population of SC neurons showed direction-selective activity before the onset of movement in response to the stimuli irrespective of stimulation modality. Trial-by-trial correlation analysis showed that the premovement activity of many SC neurons increased with faster reaction speed for the contraversive movement, whereas the premovement activity of another population of neurons decreased with faster reaction speed for the ipsiversive movement. When visual and auditory stimuli were presented simultaneously, the premovement activity of a population of neurons for the contraversive movement was enhanced, whereas the premovement activity of another population of neurons for the ipsiversive movement was depressed. Unilateral inactivation of SC using muscimol prolonged reaction times of contraversive movements, but it shortened those of ipsiversive movements. These findings suggest that the difference in activity between the SC hemispheres regulates the reaction speed of motor responses, and multisensory information enlarges the activity difference resulting in faster responses., Japan. Ministry of Education, Culture, Sports, Science and Technology (Grant-in-Aid for Scientific Research on Priority Areas (Molecular Brain Science)), Japan. Ministry of Education, Culture, Sports, Science and Technology (Grant-in-Aid for Young Scientists), Japan. Science and Technology Agency (CREST Program)

Ca2+/calmodulin-dependent protein kinase II (CaMKII) and actin are two crucial molecules involved in long-term potentiation (LTP). In addition to its signaling function, CaMKII plays a structural role via direct interaction with actin filaments, thus coupling functional and structural plasticity in dendritic spines. The status of F-actin, regulated by CaMKII, determines the postsynaptic protein binding capacity and thus may act as a synaptic tag that consolidates LTP.

The mechanism that controls the selective vulnerability of striatal neurons in Huntington's disease is unclear. Brain-derived neurotrophic factor (BDNF) protects striatal neurons and is regulated by Huntingtin through the interaction with the neuron-restrictive silencer factor. Here, we demonstrate that the downregulation of BDNF by mutant Huntingtin depends on the length and levels of expression of the CAG repeats in cell cultures. To analyze the functional effects of these changes in BDNF in Huntington's disease, we disrupted the expression of bdnf in a transgenic mouse model by cross-mating bdnf(+/ -) mice with R6/1 mice. Thus, we compared transgenic mice for mutant Huntingtin with different levels of BDNF. Using this double mutant mouse line, we show that the deficit of endogenous BDNF modulates the pathology of Huntington's disease. The decreased levels of this neurotrophin advance the onset of motor dysfunctions and produce more severe uncoordinated movements. This behavioral pathology correlates with the loss of striatal dopamine and cAMP-regulated phosphoprotein-32-positive projection neurons. In particular, the insufficient levels of BDNF cause specific degeneration of the enkephalinergic striatal projection neurons, which are the most affected cells in Huntington's disease. This neuronal dysfunction can specifically be restored by administration of exogenous BDNF. Therefore, the decrease in BDNF levels plays a key role in the specific pathology observed in Huntington's disease by inducing dysfunction of striatal enkephalinergic neurons that produce severe motor dysfunctions. Hence, administration of exogenous BDNF may delay or stop illness progression., This study was supported by Ministerio de Ciencia y Tecnología Grants SAF2002-00314 (J.A.), SAF2002-00311 (J.M.C.), and SAF1999-0123 (G.M.); Redes Temáticas de Investigación Coorporativa (G03/167, G03/210; Ministerio de Sanidad y Consumo); Fundació La Caixa; and Fundación Ramón Areces. J.R.P. is a fellow of the Ministerio de Educación, Cultura y Deporte, J.F.T.-P. is a fellow of the Fundación Gran Mariscal de Ayacucho, M.B. is a fellow of the Universitat de Barcelona, and R.M.-I. is a fellow of the Ministerio de Ciencia y Tecnología